Conventional instrument cluster dials are illuminated by incorporating a small lamp on the dial or by using light conducting transparent pointer material optically coupled to a near-by light source. In the case of the small lamp on the dial, it is expensive to provide a lamp that is sufficiently small and yet sufficiently bright to illuminate the dial.
In the case of the light conduction method for dial illumination, it is the usual practice to transmit light from a remote lamp through a transparent light guide and into the dial. Problematically, illumination in such a manner requires many reflections before reaching the dial and only a small portion of the source light is eventually received by the dial, thereby resulting in a dimly lit dial. Further, a single, cone shaped reflective surface is used to couple the light into the dial. A single reflective surface has a limited usable reflective surface area with which to couple light into the dial. The limited surface area in conjunction with the small portion of light being received thereby only amplifies the dimly lit dial problem.
Recent automotive designs have necessitated reducing the packaging space or depth of the instrument cluster. Reducing the cluster depth has necessitated the use of smaller, lower power lamps for back lighting the cluster and illuminating the dial. These small lamps are less bright than the larger lamps used with the previous thicker clusters, which only amplifies the dimly lit dial problem described above.
One way to remedy the lower power lamp problem is to simply add additional lamps to brighten the dial. This solution, however, adds complexity and cost to the instrument cluster.
What is desired, therefore, is a mechanism to sufficiently illuminate an instrument cluster dial, which uses a minimum number of low power lamps, thereby minimizing cost and complexity.